An OFDM nonlinear distortion suppression adaptive selection method and module

Abstract

The application relates to an OFDM nonlinear distortion suppression adaptive selection method, which comprises the following steps: obtaining a receiving end frequency domain symbol; calculating a channel estimation value of the receiving end frequency domain symbol; performing channel equalization on the receiving end frequency domain symbol by using the channel estimation value to obtain a first processing symbol; extracting a pilot symbol of the receiving end frequency domain symbol, performing channel equalization on the pilot symbol by using the channel estimation value to obtain a first pilot symbol; calculating a correlation cumulative value of a local pilot symbol and the receiving end pilot symbol; and selecting whether to perform constellation point demapping operation after canceling nonlinear distortion in the receiving end frequency domain symbol according to the correlation cumulative value size. The application can overcome the error propagation problem of the nonlinear distortion suppression algorithm based on decision reconstruction under the condition of low signal-to-noise ratio, and ensure the nonlinear distortion suppression performance of the OFDM communication system.

Description

Technical Field

[0001] This invention relates to the field of OFDM communication signal processing technology, and in particular to an adaptive selection method and module for nonlinear distortion suppression at an OFDM receiver. Background Technology

[0002] In communication systems using OFDM modulation, such as 4G, 5G, and WIFI communication, envelope soft clipping and digital predistortion combined algorithms are usually used to improve the efficiency of the transmitting power amplifier. This causes the OFDM time-domain transmitted signal waveform to be affected by nonlinear distortion, which deteriorates the bit error rate performance of the communication link. In order to improve the link performance, the receiving end can use the Decision Aid Reconstruction (DAR) algorithm based on decision reconstruction in reference [1]. This algorithm equalizes and detects all frequency-domain received symbols affected by nonlinear distortion at the receiving end, and then performs OFDM modulation to reconstruct the OFDM time-domain transmitted signal. Then, it reconstructs the time-domain signal samples affected by nonlinear distortion, suppresses the influence of nonlinear distortion, and thus achieves the purpose of improving the bit error rate performance of the communication link.

[0003] The core of decision-based reconstruction-based nonlinear distortion suppression algorithms lies in reliably reconstructing the OFDM time-domain transmitted signal and then reconstructing the originating nonlinear distortion. Existing literature indicates that under low signal-to-noise ratio (SNR) conditions, channel noise has a greater impact on receiver performance than nonlinear distortion, leading to unreliable reconstruction of the OFDM time-domain transmitted signal. If the algorithm is still used, error propagation occurs, preventing accurate reconstruction and cancellation of nonlinear distortion, thus reducing the bit error rate (BER) performance of the communication link. Furthermore, decision-based reconstruction-based nonlinear distortion suppression algorithms have high computational complexity; therefore, it is necessary to address the error propagation problem with a lower computational cost to improve the BER performance of the communication link. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an adaptive selection method and module for OFDM nonlinear distortion suppression, which can overcome the error propagation problem of nonlinear distortion suppression algorithm based on decision reconstruction and ensure the nonlinear distortion suppression performance of OFDM communication system.

[0005] The technical solution adopted by this invention to solve its technical problem is: to provide an adaptive selection method for OFDM nonlinear distortion suppression, comprising the following steps:

[0006] Obtain the frequency domain symbol at the receiving end;

[0007] Calculate the channel estimate value of the frequency domain symbol at the receiving end;

[0008] The channel estimation value is used to perform channel equalization on the frequency domain symbols at the receiving end to obtain the first processed symbol;

[0009] Extract the pilot symbol from the frequency domain symbol of the receiving end, and use the channel estimation value to perform channel equalization on the pilot symbol to obtain the first pilot symbol;

[0010] Calculate the cumulative correlation value between the local pilot symbol and the first pilot symbol;

[0011] The correlation cumulative value is compared with the threshold value. If the correlation cumulative value is less than or equal to the threshold value, the nonlinear distortion in the first processed symbol is canceled before constellation point mapping operation is performed. If the correlation cumulative value is greater than the threshold value, constellation point mapping operation is performed directly on the first processed symbol.

[0012] Furthermore, the relevant cumulative value is the accumulation of the results obtained by multiplying the first pilot symbol and the local pilot symbol by subcarrier conjugate.

[0013] Furthermore, the relevant cumulative value is calculated using the following formula.

[0014]

[0015] Where S p For the relevant cumulative value, N p Let || be the number of subcarriers of the first pilot symbol, and |·| be the modulus operation for complex numbers. Let be the set of pilot subcarrier indices in the l-th first pilot symbol. For the l-th first pilot symbol of the k-th subcarrier, It is the conjugate of the l-th local pilot symbol of the k-th subcarrier.

[0016] Furthermore, the nonlinear distortion in the first processed signal is canceled using a nonlinear distortion suppression algorithm based on decision reconstruction.

[0017] The technical solution adopted by this invention to solve its technical problem is: to provide an adaptive selection module for OFDM nonlinear distortion suppression, comprising:

[0018] The OFDM demodulation module is used to obtain the frequency domain symbols at the receiving end;

[0019] The channel estimation and equalization module is used to calculate the channel estimate value of the frequency domain symbol of the receiving end, perform channel equalization on the frequency domain symbol of the receiving end using the channel estimate value to obtain the first processed symbol, and simultaneously extract the pilot symbol of the frequency domain symbol of the receiving end, and perform channel equalization on the pilot symbol using the channel estimate value to obtain the first pilot symbol.

[0020] The correlation cumulative value calculation module is used to calculate the correlation cumulative value between the first pilot symbol and the local pilot symbol;

[0021] The nonlinear distortion suppression module is used to compare the correlation cumulative value with the threshold value. If the correlation cumulative value is less than or equal to the threshold value, the nonlinear distortion in the first processed symbol is canceled by the nonlinear distortion cancellation reconstruction algorithm based on decision reconstruction before constellation point mapping operation is performed. If the correlation cumulative value is greater than the threshold value, the constellation point mapping operation is performed directly on the first processed symbol.

[0022] Furthermore, the relevant cumulative value is the accumulation of the results obtained by multiplying the first pilot symbol and the local pilot symbol by subcarrier conjugate.

[0023] Beneficial effects

[0024] By adopting the above-mentioned technical solution, the present invention has the following advantages and positive effects compared with the prior art: The present invention extracts the pilot signal of the frequency domain signal of the receiving end, obtains the first pilot symbol after channel estimation and equalization, and then calculates the correlation cumulative value of the first pilot symbol and the local pilot symbol. By comparing the correlation cumulative value with the threshold value, the nonlinear distortion suppression algorithm based on decision reconstruction is used only when the correlation cumulative value is less than or equal to the threshold value. This solves the error propagation problem of the algorithm with a small computational complexity and improves the bit error rate performance of the communication link. Attached Figure Description

[0025] Figure 1 This is a flowchart of the first embodiment of the present invention;

[0026] Figure 2 This is a graph showing the correlation cumulative value and threshold value under different signal-to-noise ratios in the first embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the structure of the second embodiment of the present invention. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0029] The first embodiment of the present invention relates to an adaptive selection method for OFDM nonlinear distortion suppression, such as... Figure 1 As shown, it includes the following steps:

[0030] Obtain the frequency domain symbol at the receiving end;

[0031] Calculate the channel estimate for the frequency domain symbols at the receiver;

[0032] Channel equalization is performed on the frequency domain symbols at the receiving end using the channel estimation values ​​to obtain the first processed symbol;

[0033] Extract the pilot symbol from the frequency domain symbol of the receiver, and use the channel estimate to perform channel equalization on the pilot symbol to obtain the first pilot symbol;

[0034] Calculate the correlation cumulative value between the local pilot symbol and the first pilot symbol;

[0035] The correlation cumulative value is compared with the threshold value. If the correlation cumulative value is less than or equal to the threshold value, the nonlinear distortion in the frequency domain symbol at the receiving end is canceled before constellation demapping is performed. If the correlation cumulative value is greater than the threshold value, constellation demapping is performed directly on the frequency domain symbol at the receiving end.

[0036] The following section provides a further explanation of this method using CP-OFDM communication as an example, specifically including the following steps:

[0037] (1) At the OFDM communication transmitter, the cyclic prefix CP-OFDM waveform scheme is used. For any subframe, its l-th frequency domain symbol and k-th subcarrier can carry either a data symbol or a pilot symbol, as specified by the frame structure of the communication protocol. The data or pilot symbol carried by the k-th subcarrier is represented as X. l [k]. The inverse discrete Fourier transform (IFFT) has a length of N points, where l = 0, ..., L-1, k = 0, ..., N-1. Then, a cyclic prefix is ​​added and a parallel-to-serial conversion is performed to obtain the transmitter's time-domain baseband signal x[m], m = 0, ..., M-1, where M is the time-domain sample length of each subframe. After x[m] is affected by the nonlinear distortion device at the transmitter, the resulting signal containing nonlinear distortion is y[m], which is radiated to the receiver via the antenna.

[0038] (2) At the OFDM communication receiver, the received baseband signal is v[m]. First, v[m] is converted from serial to parallel to remove the cyclic prefix, and then an N-point positive discrete Fourier transform is performed to obtain the receiver frequency domain symbol V containing nonlinear distortion. l [k].

[0039] (3) For the frequency domain symbol V at the receiving end l [k] Perform channel estimation to obtain the channel estimate value, and extract the pilot received symbol V from the frequency domain symbol at the receiver. l [k], in Let l be the set of pilot subcarrier indices in the l-th frequency domain received symbol, where l = 0, ..., L-1. Equalize these indices using channel estimates to obtain the equalized pilot received symbol. Let P be the first pilot symbol, where P l [k] represents the local pilot symbol. This is the equivalent channel noise on the k-th subcarrier of the l-th frequency domain symbol after equalization. Simultaneously, the channel estimate is used to evaluate the received frequency domain symbol V. l [k] performs equalization to obtain the first processed symbol.

[0040] (4) Calculation and local pilot symbol P l The cumulative value S related to [k] p ,

[0041]

[0042] Where |·| represents the modulo operation for complex numbers. Let be the set of pilot subcarrier indices in the l-th first pilot symbol. For the l-th first pilot symbol of the k-th subcarrier, The conjugate of the l-th local pilot symbol of the k-th subcarrier, and the number of pilot subcarriers. δ w It is the cumulative value component contributed by the equivalent channel noise.

[0043] (5) Correlation cumulative value S under different channel noise conditions p The numerical curve is as follows Figure 2 As shown, the relevant cumulative value S p It can effectively reflect channel quality. After software simulation, the threshold value θ is determined using a lookup table, and then compared with the relevant cumulative value S. p The magnitude of the threshold value θ is used to select whether to cancel the nonlinear distortion in the frequency domain symbol of the receiver. If S p If S ≤ θ, then a nonlinear distortion suppression algorithm based on decision reconstruction is selected. The algorithm output is then subjected to constellation point demapping and channel decoding to obtain an estimate of the transmitter's service bits. p If the value is greater than θ, then the decision reconstruction nonlinear distortion suppression algorithm is not used; instead, the first processing symbol is directly processed. Constellation point mapping and channel decoding are performed to obtain an estimate of the transmitted service bits.

[0044] The second embodiment of the present invention relates to an OFDM nonlinear distortion suppression selection module, such as... Figure 3 As shown, it includes:

[0045] The OFDM demodulation module is used to obtain the frequency domain symbols at the receiving end;

[0046] The channel estimation and equalization module is used to calculate the channel estimate value of the frequency domain symbol at the receiving end, and to perform channel equalization on the frequency domain symbol at the receiving end using the channel estimate value to obtain the first processed symbol. At the same time, it extracts the pilot symbol of the frequency domain symbol at the receiving end, and performs channel equalization on the pilot symbol using the channel estimate value to obtain the first pilot symbol.

[0047] The correlation cumulative value calculation module is used to calculate the correlation cumulative value between the first pilot symbol and the local pilot symbol. The correlation cumulative value is the accumulation of the results obtained by multiplying the first pilot symbol and the local pilot symbol by the conjugate of the subcarrier.

[0048] The nonlinear distortion suppression module is used to compare the correlation cumulative value with the threshold value. If the correlation cumulative value is less than or equal to the threshold value, the nonlinear distortion cancellation reconstruction algorithm based on decision reconstruction is used to cancel the nonlinear distortion in the first processed symbol before performing constellation point mapping operation. If the correlation cumulative value is greater than the threshold value, the constellation point mapping operation is directly performed on the first processed symbol.

[0049] Reference [1]: Dukhyun Kim and GLStuber, "Clipping noise mitigation for OFDM by decision-aided reconstruction," IEEE Communications Letters, vol.3, no.1, pp.4-6, Jan.1999, doi:10.1109 / 4234.740112.

Claims

1. An adaptive selection method for OFDM nonlinear distortion suppression, characterized in that, Includes the following steps: Obtain the frequency domain symbol at the receiving end; Calculate the channel estimate value of the frequency domain symbol at the receiving end; The channel estimation value is used to perform channel equalization on the frequency domain symbols at the receiving end to obtain the first processed symbol; Extract the pilot symbol from the frequency domain symbol of the receiving end, and use the channel estimation value to perform channel equalization on the pilot symbol to obtain the first pilot symbol; Calculate the cumulative correlation value between the local pilot symbol and the first pilot symbol; The relevant cumulative value is the accumulation of the results obtained by multiplying the first pilot symbol and the local pilot symbol by subcarrier conjugate, and is calculated as follows: in, For the relevant cumulative value, The number of subcarriers of the first pilot symbol. For the modulo operation of complex numbers, For the first The set of pilot subcarrier indices in the first pilot symbol For the first The first subcarrier The first pilot symbol, For the first The first subcarrier The conjugate of each of the local pilot symbols; The correlation cumulative value is compared with the threshold value. If the correlation cumulative value is less than or equal to the threshold value, the nonlinear distortion in the first processed symbol is canceled before constellation point mapping operation is performed. If the correlation cumulative value is greater than the threshold value, constellation point mapping operation is performed directly on the first processed symbol.

2. The method according to claim 1, characterized in that, The nonlinear distortion in the first processed symbol is canceled out by a nonlinear distortion suppression algorithm based on decision reconstruction.

3. An adaptive selection module for OFDM nonlinear distortion suppression, characterized in that, include: The OFDM demodulation module is used to obtain the frequency domain symbols at the receiving end; The channel estimation and equalization module is used to calculate the channel estimate value of the frequency domain symbol of the receiving end, perform channel equalization on the frequency domain symbol of the receiving end using the channel estimate value to obtain the first processed symbol, and simultaneously extract the pilot symbol of the frequency domain symbol of the receiving end, and perform channel equalization on the pilot symbol using the channel estimate value to obtain the first pilot symbol. The correlation cumulative value calculation module is used to calculate the correlation cumulative value based on the first pilot symbol and the local pilot symbol; the correlation cumulative value is the accumulation of the results obtained by multiplying the first pilot symbol and the local pilot symbol by subcarrier conjugate, and the calculation method is as follows: in, For the relevant cumulative value, The number of subcarriers of the first pilot symbol. For the modulo operation of complex numbers, For the first The set of pilot subcarrier indices in the first pilot symbol For the first The first subcarrier The first pilot symbol, For the first The first subcarrier The conjugate of each of the local pilot symbols; The nonlinear distortion suppression module is used to compare the correlation cumulative value with the threshold value. If the correlation cumulative value is less than or equal to the threshold value, the nonlinear distortion in the first processed symbol is canceled by the nonlinear distortion cancellation reconstruction algorithm based on decision reconstruction before constellation point mapping operation is performed. If the correlation cumulative value is greater than the threshold value, the constellation point mapping operation is performed directly on the first processed symbol.

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